Ganglion cysts are small, benign, fluid-filled sacs. They can be attached to joints or arise from a tendon sheath, which is the covering over the tendon.
They most commonly affect the wrist and hand, but they can appear on the ankle, foot, or knee. They form small lumps under the skin.
The cysts are not cancerous, and they are usually harmless. If they cause pain, make it hard to use the joint, or are especially unsightly, they may be removed.
Ganglion cysts mostly affect people between the ages of 15 and 40 years, and women are more susceptible than men. They are quite common, but relatively little is known about them.
Fast facts about ganglion cysts
Ganglion cysts are non-cancerous, but how they form is unclear.
Half of all ganglion cysts disappear without intervention.
The fluid within the cysts is similar to that contained within synovial joints.
Draining or surgically removing the cysts may prevent their return.
They most commonly occur next to the wrist joints, but they can affect the feet.
What is a ganglion cyst?
Ganglion cysts form a benign lump that often goes away on its own.
Ganglion cysts were first mentioned as long ago as Hippocrates, but even now, they remain something of a mystery.
They appear, often on the back of the hand, as a round or oval-shaped lump that is filled with fluid. They can range from the size of a pea to that of a golf ball.
Beneath the skin, the cyst resembles a water balloon on a stalk.
A cyst does not pose a significant medical threat, but it can sometimes be troubling.
If it pushes on a nerve, it can cause pain or make some movements difficult. It can sometimes be a cosmetic problem because of the size.
Ganglion cysts can usually be recognized by their features.
Location: They are always near a joint, most commonly the top or back of the wrist, but possibly on the palm side of the wrist, on the palm at the base of a finger, or on the top of the end joint of a finger. They may appear on the top of the foot, on the ankle, or sometimes the knee.
Pain: They may or may not be painful. If they press on a nerve, there may be pain.
Shape and size: They are roughly circular and less than 2.5 centimeters (cm) across, or up to the size of a golf ball. Some are very small. They may be felt as lumps under the skin, or they may not be noticeable at all.
They may be soft or hard, and they should move freely under the skin.
A ganglion cyst that occurs at the base of the finger may feel like a pea-sized lump under the skin.
If the cyst is on a finger joint, it may involve an arthritic spur, the skin over the cyst may be thin, and there may be a groove down the fingernail that is just above it.
Sometimes, the region around the cyst can feel numb, and grip strength can be reduced in the affected hand.
What causes a ganglion cyst is still not known, but they may happen when connective tissue breaks down around a joint. They tend to be attached to an underlying joint capsule or a tendon sheath.
They appear to grow from joints like a balloon on a stalk, and they tend to develop in areas where a joint or tendon naturally bulges out of place.
Risk factors seem to include:
Age and sex: Ganglion cysts can affect anyone at any time, but they are most commonly found to occur in females aged 15 to 40 years.
Joint or tendon injury: Areas injured in the past are more likely to develop ganglion cysts.
Overuse: People who use certain joints vigorously are more likely to develop ganglion cysts. Female gymnasts, for instance, are particularly prone.
Osteoarthritis: People with wear-and-tear arthritis in the joints nearest to the fingernail are more likely than others to develop this type of cyst.
Trauma: They may result from a single incident or from repeated small injuries.
Exactly what leads to the formation of ganglion cysts is not fully understood.
Here are three possible causes, all related to joint stress.